Method for preparing lithium sulfide based on metathesis reaction

Abstract

The invention provides a method for preparing battery-grade lithium sulfide through double decomposition reaction, which comprises the following steps: by taking lithium chloride as a lithium source compound and anhydrous sodium sulfide as a sulfur source compound, dissolving the lithium source compound and the sulfur source compound in a mixed solvent of absolute ethyl alcohol / acetonitrile, and carrying out double decomposition reaction to obtain the battery-grade lithium sulfide. The efficiency of the double decomposition reaction can be further improved by changing the feeding mode into batch adding of the sulfur source compound solution. The purity of the lithium sulfide crystal obtained by the invention meets the requirements of battery grade application; meanwhile, the reaction efficiency and the product yield can be greatly improved, and further industrial production is facilitated.

Description

Technical Field:

[0001] The present invention relates to the technical field of battery materials, and more specifically to a method for preparing lithium sulfide based on metathesis reaction. Background Art:

[0002] According to the research of authoritative institutions in the electric vehicle and related industrial chains, the global sales of new energy vehicles exceeded 14.653 million in 2023, with a year-on-year increase of 35.4%; among them, China led with 9.495 million vehicles sold. As a strong candidate for the next-generation battery technology, solid-state lithium-ion batteries have brought new hope for the development of new energy electric vehicles.

[0003] Solid electrolytes (SEs) are the core components for achieving high-performance, all-solid-state lithium batteries (ASSLBs), and their ionic conductivity and insulating properties against electrons are crucial. Currently, the research on SEs materials mainly focuses on four categories: organic polymer SEs, oxide SEs, halide SEs, and sulfide SEs. Lithium sulfide (Li 2 2S) is one of the important raw materials for sulfide SEs. Therefore, exploring a technical solution for synthesizing high-purity Li 2 2S at low cost is an important step towards the commercialization of sulfide SEs and ASSLBs.

[0004] Currently, the methods for synthesizing lithium sulfide can be classified into several types according to different lithium sources: lithium metal method, organolithium salt method, and inorganic lithium salt method. Among the inorganic lithium salt methods, the representative ones are the metathesis reaction method and the Li 2 2SO 4 4 reduction method. Among them, the metathesis reaction method is a green, safe, and efficient method for synthesizing Li 2 2S. By carrying out a metathesis reaction between relatively inexpensive lithium chloride and sodium sulfide in absolute ethanol, Li 2 2S can be obtained. The reaction equation is as follows:

[0005] Na 2 2S + 2LiCl → Li 2 2S + 2NaCl↓

[0006] The Gibbs free energy of this reaction is less than zero, and it can proceed spontaneously at room temperature. In addition, the solubility of the generated NaCl in absolute ethanol is poor, so the reaction can proceed rapidly. After filtering out NaCl, an ethanol solution of Li 2 2S can be obtained.

[0007] Patent CN112551491A discloses a method for preparing lithium sulfide. First, under the protection of an inert atmosphere, a lithium source compound and a sulfur source compound are weighed and their alcohol solutions are respectively prepared. Then, the alcohol solution of the lithium source compound is added to the alcohol solution of the sulfur source compound. After magnetic stirring, the fully reacted product is centrifuged and the supernatant is collected. Then, it is transferred to a tubular furnace for heating and crystallization to obtain a crude lithium sulfide product. Next, the crude lithium sulfide product is washed and centrifuged with N-methylpyrrolidone or acetone, and the solid product is collected. Then, the solid product is washed and centrifuged with n-hexane and dried to obtain lithium sulfide. This method can obtain lithium sulfide through a metathesis reaction, but the overall purity of this method is insufficient and the reaction efficiency is poor.

[0008] Therefore, there is an urgent need for a method for preparing battery-grade lithium sulfide through a metathesis reaction that can further improve the purity and yield. Summary of the Invention:

[0009] The present invention intends to provide a new method for preparing battery-grade lithium sulfide through a metathesis reaction to solve the practical problems of low purity and yield in the preparation of lithium sulfide by the metathesis reaction method in the prior art.

[0010] To achieve the above object, the technical idea adopted by the present invention is as follows:

[0011] Utilize the metathesis reaction principle between a sulfur source compound and a lithium source compound to prepare lithium sulfide. By improving the addition method of the reaction raw materials and the selection of the solvent, the efficiency of the metathesis reaction is further improved, thereby enhancing the yield of lithium sulfide.

[0012] The technical solution of the present invention includes the following steps:

[0013] (1) Under the protection of an inert gas, a lithium source compound and a sulfur source compound are respectively taken and dissolved in a solvent to prepare a solution; the sulfur source compound solution is added to the lithium source compound solution in batches, and magnetic stirring is carried out to obtain a suspension;

[0014] (2) Under the protection of an inert atmosphere, the suspension is centrifuged and the supernatant is collected;

[0015] (3) The supernatant is transferred to a reaction furnace, an inert atmosphere is introduced for protection, and heating and evaporation crystallization are carried out to obtain a crude lithium sulfide product;

[0016] (4) Under the protection of an inert atmosphere, the crude lithium sulfide product is washed with N-methylpyrrolidone or acetone, centrifuged, and the solid product is collected;

[0017] (5) Under the protection of an inert atmosphere, the solid product is washed with n-hexane, centrifuged, and vacuum dried to obtain lithium sulfide.

[0018] Wherein the inert atmosphere is nitrogen or argon, and the reaction furnace is a tube furnace or a muffle furnace.

[0019] Wherein, the lithium source compound in step (1) is lithium chloride, and the sulfur source compound is anhydrous sodium sulfide; the solvent is a mixed solvent of anhydrous ethanol and acetonitrile, and the volume ratio of anhydrous ethanol to acetonitrile is (6-10):1.

[0020] Preferably, the overall molar ratio of the sulfur source compound to the lithium source compound is (0.7-0.9):2. Among them, the molar ratio of the sulfur source compound to the lithium source compound added for the first time is (0.5-0.6):2; the remaining sulfur source compound is added after reacting for 4-6 h, and the stirring time is continued for 2-8 h after adding.

[0021] Wherein, in step (1), the rotation speed of the magnetic stirring is 500-800 rpm.

[0022] Wherein, in step (3), the heating condition is to preheat at 50-80 °C for 3-8 h, then raise the temperature to 200-500 °C, and continue heating for 6-24 h.

[0023] In steps (2), (4) and (5), the rotation speed of the centrifugation is 4000-10000 rpm, and the time is 5-30 min.

[0024] In the present invention, by adopting the method of adding the sulfur source compound in batches, it can effectively ensure that the lithium source compound in the reaction system is always in an excessive state. This design can not only fully consume the sulfur source compound, but also make the generated NaCl easier to precipitate due to the higher chloride ion concentration in the system, thereby further promoting the reaction.

[0025] Secondly, the present invention optimizes the solvent system, replacing the single anhydrous ethanol with a mixed solvent of anhydrous ethanol and acetonitrile. This improvement significantly reduces the solubility of NaCl in the solvent, while not affecting the solubility of the lithium source compound and the sulfur source compound in the solvent, thereby further promoting the reaction. Compared with the prior art, the present invention has the following beneficial effects:

[0026] By adding the sulfur source compound in batches, it is ensured that the lithium source compound is always in a relatively high proportion in the initial and middle stages of the reaction, thereby fully consuming the sulfur source compound and improving the reaction efficiency. The use of a mixed solvent of anhydrous ethanol and acetonitrile significantly reduces the solubility of NaCl, while not affecting the solubility of the reactants, further promoting the reaction. Through the above technical improvements, the present invention significantly improves the synthesis efficiency of lithium sulfide, providing a more efficient and economical solution for industrial production. Specific embodiments:

[0027] To make the purpose, technical solution and advantages of the implementation of the present invention clearer, the technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should be aware that the embodiments are only for helping to understand the technical content and technical effects of the present invention and should not be regarded as a limitation of the present invention.

[0028] Example 1

[0029] (1) Inside a nitrogen atmosphere glove box, weigh according to the overall molar ratio of anhydrous sodium sulfide and lithium chloride of 0.8:2. Weigh 19.5 g and 11.7 g of sodium sulfide (molar ratio 5:3), and add them to 2 L and 1 L of a mixed solvent of anhydrous ethanol / acetonitrile (volume ratio 9:1) respectively, and stir magnetically at a rotation speed of 600 rpm for 30 min. Weigh 42.4 g of lithium chloride, add it to 1.5 L of a mixed solvent of anhydrous ethanol / acetonitrile (volume ratio 9:1), stir magnetically at a rotation speed of 600 rpm for 20 min. Add the solution containing 19.5 g of sodium sulfide to the lithium chloride solution, and continue to stir for 4 h under the condition of a rotation speed of 600 rpm. Then, add the solution containing 11.7 g of sodium sulfide to the reaction again and react for another 4 h to obtain a suspension.

[0030] (2) After the reaction is complete, under nitrogen atmosphere protection, transfer the suspension to a centrifuge tube for centrifugation. Set the centrifuge rotation speed to 8000 rpm and the time to 15 min.

[0031] (3) Under nitrogen atmosphere protection, use a dropper to transfer the supernatant to a porcelain boat, and transfer it to a nitrogen-protected tube furnace. Preheat at 70 °C for 4 h, then heat up to 300 °C at a rate of 5 °C / min, and continue to heat for 8 h to allow lithium sulfide to crystallize fully, obtaining a crude lithium sulfide product containing a small amount of lithium chloride.

[0032] (4) Under nitrogen atmosphere, wash the crude product with N-methylpyrrolidone, then centrifuge at a centrifuge rotation speed of 8000 rpm for 15 min, and collect the solid product.

[0033] (5) Take the solid product and wash it with n-hexane and centrifuge under nitrogen atmosphere protection. Set the centrifuge rotation speed to 8000 rpm and the time to 10 min, and repeat twice. Finally, dry it under vacuum to obtain the lithium sulfide product. Weigh the obtained lithium sulfide product, and the result is 17.6 g, and the yield is 95.6%.

[0034] Example 2

[0035] (1) Inside a nitrogen atmosphere glove box, weigh according to the molar ratio of anhydrous sodium sulfide to lithium chloride of 0.8:2. Weigh 23.4 g and 7.8 g of sodium sulfide (molar ratio 6:2) respectively, and add them to 2.4 L and 0.8 L of a mixed solvent of anhydrous ethanol / acetonitrile (volume ratio 7:1) respectively. Stir magnetically at a speed of 500 rpm for 30 min. Weigh 42.4 g of lithium chloride and add it to 1.2 L of a mixed solvent of anhydrous ethanol / acetonitrile (volume ratio 7:1), stir magnetically at a speed of 500 rpm for 30 min. Add the solution containing 23.4 g of sodium sulfide to the lithium chloride solution, and continue to stir for 6 h under the condition of 500 rpm. Then add the solution containing 7.8 g of sodium sulfide to the reaction again and react for another 4 h to obtain a suspension.

[0036] (2) After the reaction is complete, under nitrogen atmosphere protection, transfer the suspension to a centrifuge tube and centrifuge. Set the centrifuge speed to 6000 rpm for 20 min.

[0037] (3) Under nitrogen atmosphere protection, use a dropper to transfer the supernatant to a porcelain boat, and transfer it to a nitrogen-protected tubular furnace. Preheat at 60 °C for 4 h, then heat up to 250 °C at a rate of 5 °C / min, and continue to heat for 12 h to allow lithium sulfide to crystallize fully, obtaining a crude lithium sulfide product containing a small amount of lithium chloride.

[0038] (4) Under nitrogen atmosphere, wash the crude product with N-methylpyrrolidone, then centrifuge at a centrifuge speed of 8000 rpm for 10 min, and collect the solid product.

[0039] (5) Take the solid product and wash it with n-hexane and centrifuge under argon atmosphere protection. Set the centrifuge speed to 8000 rpm for 10 min, and repeat twice. Finally, dry it under vacuum to obtain the lithium sulfide product. Weigh the obtained lithium sulfide product, and the result is 17.4 g, with a yield of 94.5%.

[0040] Comparative Example 1

[0041] The preparation method is the same as that in Example 1, except that some steps in step (1) are changed to: dissolve 31.2 g of sodium sulfide in 3 L of an anhydrous ethanol / acetonitrile (volume ratio 9:1) solvent to prepare a sodium sulfide solution, add the sodium sulfide solution to the lithium chloride solution, and continuously stir and react for 8 hours to obtain a suspension.

[0042] Weigh the obtained lithium sulfide product, and the result is 15.8 g, with a yield of 85.8%.

[0043] Comparative Example 2

[0044] The preparation method is the same as that of Example 1, except that the anhydrous ethanol / acetonitrile (volume ratio 9:1) solvent in step (1) is replaced with anhydrous ethanol.

[0045] The obtained lithium sulfide product was weighed to be 16.1 g, with a yield of 87.5%.

[0046] The purity of the lithium sulfide prepared in the above Examples 1-2 was tested, and the purity of the prepared lithium sulfide crystals reached 99.99%, meeting the requirements of battery-grade lithium sulfide, and the actual yield reached more than 94%, greatly saving costs.

[0047] Comparing Example 1 with Comparative Example 1, since sodium sulfide is added twice, the lithium source compound is in a higher proportion in the early and middle stages of the reaction, so that the sulfur source compound in the reaction system can be fully consumed, and the yield of lithium sulfide is greatly improved.

[0048] From Example 1 and Comparative Example 2, replacing anhydrous ethanol with a mixture of anhydrous ethanol / acetonitrile further reduces the solubility of NaCl in the solvent, while not affecting the solubility of the lithium source compound and the sulfur source compound therein, thereby promoting further reaction and greatly improving the yield of lithium sulfide.

[0049] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing battery-grade lithium sulfide based on double decomposition reaction, characterized in that: The steps include: (1) Under the protection of an inert gas, a lithium source compound and a sulfur source compound are respectively dissolved in a solvent to prepare a solution; the sulfur source compound solution is added to the lithium source compound solution in batches, and magnetic stirring is performed to obtain a suspension; (2) under the protection of an inert atmosphere, centrifuging the suspension and collecting the supernatant; (3) transferring the supernatant to a reaction furnace, introducing an inert atmosphere for protection, heating for evaporation and crystallization, and obtaining a crude lithium sulfide product; (4) under the protection of an inert atmosphere, washing the crude lithium sulfide product with N-methylpyrrolidone or acetone, centrifuging, and collecting a solid product; (5) Under the protection of an inert atmosphere, the solid product is washed with n-hexane, centrifuged, and vacuum dried to obtain lithium sulfide.

2. The method according to claim 1, characterized in that The inert atmosphere is nitrogen or argon, and the reaction furnace is a tubular furnace or a muffle furnace.

3. The method according to claim 1, characterized in that: The lithium source compound in step (1) is lithium chloride, and the sulfur source compound is anhydrous sodium sulfide; the solvent is a mixed solvent of anhydrous ethanol and acetonitrile, wherein the volume ratio of anhydrous ethanol to acetonitrile is (6-10):

1.

4. The method according to claim 1, characterized in that: The overall molar ratio of the sulfur source compound to the lithium source compound is (0.7-0.9):

2.

5. The method according to claim 4, characterized in that: The molar ratio of the first added sulfur source compound to the lithium source compound is (0.5-0.6):2; the remaining sulfur source compounds are added after the reaction for 4-6 hours, and the stirring time after addition is continued for 2-8 hours.

6. The method according to claim 1, characterized in that In step (1), the rotation speed of the magnetic stirring is 500-800 rpm.

7. The method according to claim 1, characterized in that In step (3), the heating conditions are preheating at 50-80°C for 3-8h, then heating to 200-500°C, and continuing heating for 6-24h.

8. The method according to claim 1, characterized in that In steps (2), (4) and (5), the centrifugal speed is 4000-10000 rpm and the time is 5-30 min.